A rotary traveling wave oscillator is described in U.S. Pat. No. 6,556,089, which is incorporated by reference into the present application. In that patent, a wavefront moves around a closed, differential loop, reversing its polarity in each transit of the loop. The wavefront traveling on the loop is established and maintained by a plurality of regeneration elements, such as back-to-back inverters, distributed about the entire loop, in one embodiment. FIG. 1 shows an embodiment 10 of a back-to-back inverter 12, 14. The result of this arrangement is that at any point on the differential loop, a differential clock signal is available. The frequency of the clock signal is determined by the electrical size of the loop, by which is meant the time it takes to make a lapse around the loop, given the loop's loaded transmission line characteristics.
PCT/GB01/02069, which is incorporated by reference into the present application, describes an embodiment, shown in FIG. 12B, in which circuitry biases the wave so that it travels in a preferred direction, either clockwise or counter clockwise. According to this application, the direction of the traveling wave is not changeable once the wave had been established on the loop. See PCT/GB01/02069, page 7, lines 24-25. That is, to change the direction of the wave, one would have to cycle power the loop and re-start the wave in the opposite direction. While this startup circuitry accomplishes the function of assuring that the traveling wave moves in a preferred direction, it would be desirable to establish the direction of the traveling wave without cycling power the loop, i.e., to change the direction of the wave in real time.